Flip-chip ball grid array (FCBGA) semiconductor package combines flip-chip and ball-grid-array structures, wherein at least one semiconductor chip is incorporated in a flip-chip manner that an active surface of the chip is electrically connected to a side of a substrate via a plurality of conductive bumps, and a plurality of solder balls are formed on an opposite side of the substrate to serve as input/output (I/O) connections. This FCBGA package desirably has a reduced size and improved electrical performance as not requiring the use of bonding wires, thereby reducing the resistance and preventing signal degradation during transmission, such that the FCBGA package becomes one of the most popular package technologies in the next generation.
Due to the above advantageous characteristics such as the reduced size and improved performance, the FCBGA package is widely used for packaging highly integrated semiconductor chips. Since such highly-integrated chips usually produce a large amount of heat during the high-frequency operation thereof, how to effectively dissipate heat plays a key role in determining the lifetime of the chips and the yield of the fabricated packages.
In order to improve the heat dissipating efficiency for the FCBGA package, it is common to attach at least one embedded heat spreader to the flip chip mounted on the chip carrier such as substrate during package fabrication. This allows heat generated from the flip chip during operation to be transmitted through a non-active surface of the chip to the heat spreader and dissipated, such that the heat does not pass through a poor thermally conductive encapsulation body used for encapsulating the chip, and thus the heat dissipating efficiency of the package is improved.
U.S. Pat. No. 5,311,402 discloses a semiconductor package with a heat spreader. As shown in FIG. 6, a substrate 40 is formed with an area for accommodating a chip 42 and a plurality of grooves 401 thereon. The heat spreader 44 is attached to the substrate 40 via an adhesive 45 filled in the grooves 401, wherein a plurality of support portions 44b of the heat spreader 44 are respectively inserted in the corresponding grooves 401, such that the heat spreader 44 is secured in position on the substrate 40 by means of the adhesive 45. This method to insert the support portions 44b in the grooves 401 desirably increases the contact area between the heat spreader 44 and the substrate 40, thereby avoiding a problem that the bonding strength would be reduced due to insufficient contact area. However, forming grooves 401 on the substrate 40 not only complicates the fabrication processes and increases the fabrication cost, but also damages the structure of the substrate 40 thereby easily leading to a reliability issue.
Accordingly, there is developed an alternative method to form grooves on the support portions of the heat spreader instead of on the substrate. As shown in a semiconductor package of FIG. 7, besides areas for accommodating a chip 52 and conductive traces, one or more heat spreader bonding areas 500 are defined on a substrate 50 for mounting a heat spreader 54. The heat spreader 54 comprises a flat portion 54a and a plurality of support portions 54b for supporting the flat portion 54a above the chip 52. One or more grooves 57 are formed on the support portions 54b at areas for contacting the heat spreader bonding areas 500 on the substrate 50. This allows a fluid adhesive 55 to be filled into the grooves 57 and between the support portions 54b and the heat spreader bonding areas 500 so as to firmly attach the heat spreader 54 to the substrate 50 when the adhesive 55 is cured.
Forming grooves 57 on the support portions 54b of the heat spreader 54 for receiving the adhesive 55 desirably provides an anchoring effect to enhance the bonding strength between the heat spreader 54 and the substrate 50. However, the adhesive 55 filled into the grooves 57 seals the grooves 57, and makes air trapped in the groove 57 and not able to be dissipated. As a result, during temperature cycles of subsequent fabrication processes, the air trapped in the grooves 57 would cause a popcorn effect that reduces the adhesion reliability between the heat spreader 54 and the substrate 50.
Moreover, it is difficult to observe from the appearance and examine the amount of adhesive filled in the grooves. If an excess amount of adhesive is applied, the adhesive would contaminate the substrate. On the contrary, if the amount of adhesive used is insufficient, it results in air trapped in the grooves and causes the popcorn effect.
Therefore, the problem to be solved here is to provide a heat dissipating structure for use in a semiconductor package, which allows an amount of adhesive used for the heat dissipating structure to be determined from the appearance of the heat dissipating structure.